Rendering is an industrial process that converts raw materials into stable, value-added materials. The process involves heating or cooking of raw materials to liquefy and separate fat from animal tissues. The majority of tissue processed comes from slaughterhouses but also includes restaurant grease and butcher shop trimmings. This material can include the fatty tissue, bones, and offal, as well as entire carcasses of animals condemned at slaughterhouses, and those that have died on farms or in transit. The most common animal sources are beef, pork, sheep, poultry and fish.
Generally, the rendering process is accomplished by receiving raw materials, such as animal byproduct materials, followed by removing undesirable parts, cutting, mixing, cooking and separating fat and protein materials. The concentrated protein is then dried and ground. The rendering process yields a fat commodity and a protein meal. Additionally, refining of gases, odors, and wastewater is necessary. After rendering, the materials are much more resistant to spoiling. The fat can be used in animal feed, as a raw material for biodiesel production, and as a feed-stock for the chemical industry. The bone and protein becomes dry particles known as meat and bone meal, and can be fed to certain animals.
FIG. 1 discloses a conventional apparatus 100 utilized in an animal byproduct rendering process. Raw material to be rendered is received for temporary storage in raw material bins 120. The raw material is then conveyed to a raw material grinder 125 that reduces the raw material to a uniform particle size for material handling and improved heat transfer for cooking. The ground raw material is fed into a cooker 130. The cooker 130 is heated by a boiler 135 generating boiler steam. The boiler brings the raw material to a predetermined and elevated temperature, evaporating moisture and freeing fat from protein and bone. A dehydrated slurry of fat and solids is discharged from the cooker 130 at a controlled rate. The discharged slurry is transported to an oil drainer 160. The drainer 160 separates liquid fat from the solids. The liquid fat is pumped to an oil centrifuge 165, which removes impurities from the fat. The fat is transported to the storage 168 as finished fat. The solids from the drainer 160 go to the presses 170, which reduce the solids' fat content further. Solids discharged from the presses go to a grinding room 175, a hammermill 180, and a screener 185 for further screening and processing of the solids, where they are transported to the storage 190 as a finished product.
Still referring to FIG. 1, water vapor exits the cooker 130 to a condenser 150, which condenses the water vapor. The condensed vapors are eventually discharged as waste water. Odorous gases generated at various points in the rendering process are collected for neutralization and removal by a scrubber 140.
The conventional rendering process of FIG. 1 has several disadvantages. Cookers generate strong odors and the cookers use in the rendering process requires expensive odor control equipment, such as scrubbers, condensers and waste water storage. These odor-control and odor-causing sources require increased personnel labor, water use, energy consumption, and adequate cooling capacity, in addition to their costs.
U.S. Pat. No. 5,759,568 describes a method of processing a waste water stream into animal foodstuffs. The '568 patent is based on addition of bentonite and a polymer to a food processing plant's waste water stream. The '568 patent describes the process as a combination of, at least, three aqueous streams, so that the final stream can be substantially diluted. This is confirmed by the use of a flotation vessel for solids-water separation, resulting in the discharge of the effluent into the sewer system. A drawback of the invention is that the flotation process results in separated solids containing abundant moisture, and the effluent containing residual suspended solids. The bentonite material has to be hydrated prior to mixing with the waste water stream. The '568 patent is thus limited to diluted waste water streams. The '568 patent also uses filter presses for sludge dewatering that significantly adds to the cost of the process.